In a typical high power battery protection circuit, a charging switch and a discharging switch are employed to control the charging loop and the discharging loop, respectively. In addition, an external resistor and a pre-charging switch are used for pre-charging purposes.
Prior Art FIG. 1 shows a typical battery protection circuit 100 able to perform pre-charge, in accordance with the prior art. The discharging switch 112 controls the discharging loop and the charging switch 110 controls the charging loop. The pre-charging switch 214 controls the pre-charging loop.
During pre-charging, the controller 102 sinks a current through the PCHG pin to switch on the switch 116. Therefore, the gate of the pre-charging switch is coupled to the positive terminal of the battery. As such, the pre-charging switch 214 is switched on accordingly to pre-charge the battery.
However, when the battery voltage is too low, the controller is not operable and is not able to sink enough current to switch on the switch 116. In other words, the pre-charging switch can not be switched on to pre-charge the battery when the battery voltage is too low or zero.